wrote:
I have been having a lot of cracking/pinging in some of my bisque
ware, and I am wondering if anyone has advice on what rate I should
ramp down. I am firing in a gas kiln, 4 burners, and it's about 8
cubic feet. I am doing cone 05 for bisque, to then fire to cone 5,
and using Laguna B-mix, no sand, and also Hagi porcelain. In the
trouble shooting notes about the clay, they say one reason for cracks
can be from cooling down to fast, what isn't there is any advice on
how to go about the cool down. I usually don't control the cool down,
I just let the kiln sitter trip, and maybe damper down.

What I plan to do with my next bisque fire is put a higher bar in the
kiln sitter, a cone 06, keep my eye on the witness cones that will be
cone 04 & 05, then when cone 05 bends I will turn down the kiln, not
turn it off. My question is, about how much should I lower the temp,
and in what sorta time increments?
Thanks
Sa

Well, first, the cones with a 0 on it get hotter in reverse of how
you're suggesting--Cone 06 is cooler than cone 05. When you rise above
cone 01 it switches to the way that makes sense...
With a gas kiln, dampering down is essential for cooling, as the draft
would shock pots going through the quartz inversion temperature. You
shouldn't have to fire down, but you might have to block both input and
exhaust areas to keep it from cooling too fast. I think that's probably
the reason most folks bisque with electricity...
Brad Sondahl

--
visit Sondahl.com for original art, music, pottery, photography,
literature, videos and more.
To respond directly, don't forget to take out the "garbage"